1. Field of Invention
The present invention relates to a back light module and a liquid crystal display (LCD).
2. Description of Related Art
FIG. 1 is a schematic view illustrating a conventional side type back light module. Referring to FIG. 1, a side type back light module 100 includes a reflector 110, a light emitting unit 120, a light guide 130, and an optical film set 140. Here, the light guide 130 has a light incident plane 114 and a light emitting plane 116, while the light emitting unit 120 is disposed next to the light incident plane 114 of the light guide 130. In addition, the optical film set 140 is disposed on the light emitting plane 116 of the light guide 130. Light emitted from the light emitting unit 120 directly enters the light guide 130 or enters the light guide 130 after the light is reflected by the reflector 110. After that, the light is irradiated from the light emitting plane 116 of the light guide 130. The light guide 130 converts the light emitted from the light emitting unit 120 from a linear light source or a point light source to a planar light source. On the other hand, the light emitting unit 120 can be formed by a cold cathode fluorescent lamp (CCFL) or a plurality of light emitting diodes (LEDs).
The light of the light emitting unit 120 is scattered and discharged out of the light emitting plane 116. Due to various polarizations, a portion of the light emitted from the light emitting unit 120 cannot be directly utilized by the LCD panel. Hence, the optical film set 140 is often required by the back light module 100 for improving light emission characteristics. In detail, the optical film set 140 includes a diffuser film 142, a prism film 144, another prism film 146, and a reflective polarized light enhancement film 148. The diffuser film 142 enables the light to be uniformly distributed, while the prism films 144 and 146 concentrate radiation directions of the emitted light. Additionally, the reflective polarized light enhancement film 148 ensures the light to be emitted out of the back light module 100 in a certain polarization direction, and the light which is not able to be irradiated is reflected back to the back light module 100. The light which is reflected back to the back light module 100 would pass through the light guide 130 and some optical films including the diffuser film 142 and the prism films 144 and 146 after reflected again by the reflector 110. Here, a portion of the light is again transformed to be in the aforesaid polarization direction and emitted out of the back light module 100. The light undergoes the recycling process by using the reflective polarized light enhancement film 148, such that the light can be reused over and over again, and thereby the luminance of the emitted light is increased. Nevertheless, the light would be lost after traveling through the optical films back and forth for a couple of times. As such, the utilization of said light in the conventional back light module 100 is not optimized.